Oxygen complexes, reactivity

Schmidt reaction of ketones, 7, 530 from thienylnitrenes, 4, 820 tautomers, 7, 492 thermal reactions, 7, 503 transition metal complexes reactivity, 7, 28 tungsten complexes, 7, 523 UV spectra, 7, 501 X-ray analysis, 7, 494 1 H-Azepines conformation, 7, 492 cycloaddition reactions, 7, 520, 522 dimerization, 7, 508 H NMR, 7, 495 isomerization, 7, 519 metal complexes, 7, 512 photoaddition reactions with oxygen, 7, 523 protonation, 7, 509 ring contractions, 7, 506 sigmatropic rearrangements, 7, 506 stability, 7, 492 N-substituted mass spectra, 7, 501 rearrangements, 7, 504 synthesis, 7, 536-537... 

Table 2 The reactivity of complexes [M(triphos)(catecholate)J+ (M=Co, Rh, Ir) with molecular oxygen as a function of the catecholate/ semiquinone oxidation potential. I=no reactivity 11= the oxygenated complex regenerates the initial complex in the quinone form by release of superoxide ion III = the oxygenated complex regenerates the initial complex in the quinone form by release of molecular oxygen...

The writers have found in their laboratory that invariably after a certain burnoff (depending upon the reactor, temperature, and sample), a subsequent extended period of constant reaction rate, expressed in grams of carbon reacting per unit time, is attained. In this bumoff region, there obviously is equilibrium between the rate of formation of the surface-oxygen complex and its removal with a carbon atom. It is felt that this is the reaction rate most characteristic of a given temperature and should be used in kinetic calculations. In principle, Wicke (31) concurs with this reasoning and reports reactivity data only after the sample has attained a total surface area which is virtually constant. 

P-450-catalyzed hydroxylations of aliphatic C—H bonds most often involve a nonconcerted mechanism (Figure 8), which occurs in two steps (1) an abstraction of the hydrogen atom by the P-450 active oxygen complex, which exhibits a free radical-like reactivity, and (2) an oxidation of the substrate-derived free radical formed in this step by the Fe(IV)—OH intermediate [34,37,38],... 

The reactivity of the molecular fullerene solid resembles the expected pattern for a homogeneous material. Only a small prereactivity at 700 K indicates that a fullcrcne-oxygen complex [12] is formed as an intermediate stoichiometric compound [15, 105], At 723 K the formation of this compound and the complete oxidation are in a steady state [12, 106, 107] with the consequence of a stable rate of oxidation which is nearly independent of the bum-off of the fullerene solid. This solid transforms prior to oxidation into a disordered polymeric material. The process is an example of the alternative reaction scenario sketched above for the graphite oxidation reaction. The simultaneous oxidation of many individual fullerene molecules. leaving behind open cages with radical centers, is the reason for the polymerization. 

It is noteworthy that the enzyme docs not activate the hydrocarbon, but rather generates a very active oxygen complex [3] a coordinated hydroxyl radical would be the reactive species and its selectivity w ould be the result of the precise proteinic environment of the catalytic center. 

The reaction with molecular oxygen gives an jj -peroxy complex, [Pt(jj -02)(PPh3)2], in which the oxygen is reactive, and the complex can oxidize PPhs, RNC, and alkenes to OPPh3, RNCO, and the epoxide. SO2, NO2, NO, and CO2 react to give the sulphate, dinitrato, dinitro, and carbonate complexes. The dioxygen complex is planar and seems to have substantial Pt character. ... 

The existence of surface metal-oxygen bonds can also be indirectly deduced by the reachvity of these bonds with molecules from the gas phase, such as the surface hydration producing new hydroxyls, the surface carbonation producing carbonates, and also some more complex reactivity, such as the reactivity with alkoxysilanes producing surface alkoxides that may later be converted to surface hydroxides by ehminahon [81]. 

A similar methodology has already been employed to characterise catalysts with several adsorbates (i.e., H2, alkanes, etc.), but not to determine the so-called active surface area of different carbon materials. The three methods presented in this work evaluate the total active surface area. No distinction is made, at this point, between reactive surface area (RSA) and stable oxygen complexes [8]. The nomenclature of ASA instead of TASA will be used for simplification. The ASA values (m g ) were calculated using the equation first proposed by Laine et al. [9]. 

Peroxo complexes Structure D(O-O) (A). -(O-O) (cm" ) Oxygen Source Reactivity and lor refs. 

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